1. Field of the Invention
The present invention relates to an ink-jet recording apparatus. Particularly, the present invention relates to an ink-jet recording apparatus in which an ink supply system, for supplying ink to an ink-jet recording head for ejecting ink for the formation of characters, images, etc., has an improved recovery device for recovering the function of the recording head by applying pressure to ink when clogging has occurred in the recording head due to dried ink, dust particles or the like.
2. Related Background Art
In a conventional ink-jet recording apparatus having an ink supply system for supplying ink to an ink-jet recording head for ejecting ink, satisfactory ejection of ink may become impossible when ink within an ejection nozzle dries due to a long interval between printing operations, or when ink is contaminated with impurities such as dust, or when bubbles have entered the recording head ink chamber. In this case, an operation for causing the recording head to recover its function is performed. A recovery operation utilizes either pressurization recovery, in which a pressurizing force created by a pump is applied to the ink so that ink within the nozzle is forced out, or suction recovery, in which cap is brought into tight contact with the nozzle and a sucking force created by a pump is applied to generate a negative pressure within the cap so that ink within the nozzle is drawn out. A pressurization recovery operation employs a pump such as a plunger (piston) pump, a gear pump or a turbine pump. Such pumps fall into two types: the type in which ink, passed through the interior of the pump itself, is directly pressurized (hereinafter referred to as "the direct pressurization type"); and the type in which the pump pressurizes air and the air pressurizes ink (hereinafter referred to as "the indirect pressurization type"). Hitherto, a pump of the direct pressurization type has often been arranged between the ink container (comprising an ink tank or ink cartridge) and the recording head. A pump of the indirect pressurization type has often been arranged to directly connect with a tightly-sealed ink tank (cartridge) so that the air within the ink tank may be pressurized to force out ink.
An ink-jet recording head may have ink-ejection nozzles arranged at a high density, such as in the case of an ink-jet recording head in a bubble-jet recording system in which heaters, provided inwardly of the nozzles, generate heat to cause a change in the state of ink, and pressure generated thereby is utilized to eject ink. A pressurization recovery operation has the following problems when dealing with the above kind of ink-jet recording head: If a direct pressurization type of pump arranged between the ink tank and the head is employed, after a long period of use, nozzles as well as filters provided between the nozzles and the ink tank tend to be clogged with particles conveyed from sliding portions of the pump. An indirect pressurization type of pump for pressurizing the air within a tightly-sealed ink tank can face problems when the amount of ink contained in the ink tank has decreased and, accordingly, a relatively large amount of air is present inside the tank. In such circumstances, the delivery of a fixed amount of air for pressurizing the ink may fail to cause a predetermined pressure to be applied to the ink within a sufficiently short period of time, or may fail to provide the desired pressure.